1. Field of the Invention
This invention relates generally to double containment pipelines having a primary pipeline within a secondary pipeline interconnecting two or more sumps, and, more particularly, to an improved double containment piping system and a centralization seal therefor that both secures the primary pipeline within and permits pressure testing of the secondary pipeline.
2. Description of the Related Art
Underground pumping systems are generally utilized in gasoline stations and other installations to transfer fluids from storage tanks to dispensing pumps through pipelines. In initial installations, the underground systems incorporated pipelines that included single wall pipes connected together at the installation with associated fittings. The pipelines were formed from pipes extending from a fitting in a storage tank sump chamber to a second fitting in a dispensing sump chamber and from there to a dispenser. Any leakage from a sump fitting would cause fluid to flow to the bottom of the sump. While the sumps provided an area that could be viewed from above to determine whether the adjacent fitting had leaked, the underground storage tanks, the pipelines, and the dispensing tanks also proved to be sources of environmental pollution, as well as safety hazards, resulting from the leakage of fuel into the surrounding earth.
To minimize these hazards, double containment systems were developed in which the primary pipeline is surrounded by a secondary pipeline. The secondary pipe has a larger diameter than the primary pipe to enable the secondary pipe to slide over the primary pipe or the primary pipe to slide through the secondary pipe during installation, as the case may be. In general, the secondary fittings are installed around the primary fittings and the secondary fittings serve as the only means for centering the primary pipeline within the secondary pipeline. However, pressure spikes in the primary pipeline can occur which might cause it to impact the secondary pipeline, resulting in damage to one or both pipelines. This is particularly common with secondary containment systems that include flexible primary pipelines that are encapsulated in metal jackets.
Further, to minimize environmental and safety hazards, secondary containment systems should be tested prior to finalization and periodically retested to ensure their integrity. In the past, secondary pipelines have not been pressure tested because the ends of each section of secondary pipeline have terminated within the open area of a sump. By necessity, sumps have an opening to the surface of the ground above, to permit access and visual inspection to determine if any fluid has leaked from the primary pipeline and been collected by the secondary pipeline. However, this opening makes air pressure testing of the secondary pipeline difficult, if not totally impractical, because the secondary pipeline is not an inherently airtight system.
Accordingly, there is a need to control movement of the primary pipeline within the secondary pipeline to prevent impact damage caused by pressure spikes and for a testing system that permits efficient and reliable air pressure testing of the secondary pipeline to assure its integrity. The present invention fulfills these needs.